DEV: Record coverage in subprocesses as well

[stefan6419846]

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 94.71%. Comparing base (e35df5a) to head (fd83294).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2556   +/-   ##
=======================================
  Coverage   94.71%   94.71%           
=======================================
  Files          50       50           
  Lines        8237     8237           
  Branches     1646     1646           
=======================================
  Hits         7802     7802           
  Misses        267      267           
  Partials      168      168           

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[stefan6419846]

Somehow GitHub does not seem to pick up the configuration - running COVERAGE_PROCESS_START=pyproject.toml python -m pytest tests --cov=pypdf --cov-append -n auto -vv locally does indeed show a difference.